feat: implement useOperations() - fetch operations for an account or tx

[omosvico]

Closes dark-princezz#125

Implements useOperations() hook that fetches operations from Horizon for a given account or transaction.

// Fetch operations for an account
const { operations, isLoading } = useOperations({
  accountId: "G...",
  limit: 20,
});

// Fetch operations for a transaction
const { operations } = useOperations({
  transactionHash: "abc...",
});

Supports cursor, limit, order, enabled, and refetchInterval options.